Create from Usage: Make extension functions/properties 'private' by default

#KT-11799 Fixed

idea/testData/quickfix/createFromUsage/createFunction/set/createSetFromUsage2.kt.after

@@ -9,6 +9,6 @@ class Foo<T> {
     }
 }
 
-operator fun <T> Any.set(s: String, w: ArrayList<T>, value: ArrayList<T>) {
+private operator fun <T> Any.set(s: String, w: ArrayList<T>, value: ArrayList<T>) {
     TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
 }